Many electrochemical cells show great promise for future power storage applications due to their high efficiency, low emissions and relatively long life. These batteries can be used in, for instance, the electric vehicle market, portable electronics and other home and commercial applications. Lithium-ion (Li-ion) batteries are one such example of these electrochemical cells. Generally, a lithium-ion battery contains two electrodes (an anode and a cathode), an electrolyte, and a material that conducts electrons, such as a current collector. Lithium is the charge carrier. A battery stores energy during charging by moving lithium atoms into the anode. Desirable electrodes have a greater capacity for energy per weight (i.e., are more energy dense) because they can store more energy in a smaller weight and/or area footprint. Therefore, more lithium density in the anode is required for a better battery.
Historically, graphite has been used as the anode in Li-ion batteries and has a capacity of approximately 372 mAh/g. However, research has shown that silicon is the theoretically optimal storage material for lithium ions in these batteries, with a capacity of greater than 4000 mAh/g. Commonly, the silicon is contained as a thin film in the anode of the Li-ion battery. Silicon in film form will stress and detach under the insertion of lithium that occurs during charging, as the rigid silicon film expands during charging by approximately 400%. This causes the silicon to degrade over time, resulting in poor energy storage and battery performance.